Growth Inhibitor To Homogenize Nucleation and Obtain Smooth HfB₂ Thin Films by Chemical Vapor Deposition

We describe an example of a new phenomenon: the use of a growth inhibitor to homogenize nucleation and improve the smoothness of a thin film deposited by chemical vapor deposition. For many film–substrate combinations, the rate of nucleation on the substrate is slow relative to the growth rate, a situation that produces a broad distribution of island sizes and a rough surface morphology. We show an example in which this outcome is avoided by directing a second component onto the substrate that has little effect on the nucleation rate but significantly retards the island growth rate. The case studied is the growth of HfB 2 films on SiO 2 substrates using the chemical vapor deposition precursor Hf(BH 4 ) 4 with NH 3 as the inhibitor. The addition of the inhibitor increases the island density at coalescence by 50× and decreases the roughness by 10× to the subnm range. We suggest that the use of inhibitors to homogenize nucleation may be applicable to other film–substrate combinations.